This invention relates generally to subsea well apparatus of the type in which a wellhead member body is adapted to be lowered into and latched within the bore of a conductor which is mounted on the ocean floor, following which a riser is connected to the upper end of the body for extension upwardly to a drilling vessel. More particularly, it relates to improvements in apparatus of this type in which the wellhead member body is xe2x80x9cweight setxe2x80x9d in the sense that it is latched in the bore of the conductor in response to its own weight, thus avoiding the need for special running and setting tools for that purpose.
Since the riser is subject to wave and wind action, it is bent with respect to the subsea well, thus imposing bending forces on the latch and causing resulting fatigue. Various efforts have been made to stabilize latching of the wellhead member body within the conductor bore. For example, in accordance with U.S. Pat. No. 5,029,647, the wellhead member body has upper and lower downwardly and inwardly tapering wedge surfaces which are tightly received within coaxial upper and lower downwardly and inwardly tapered wedge surfaces on the conductor bore as the wellhead member is lowered and latched within the conductor by upwardly facing ratchet teeth on the conductor engageable with ratchet grooves on the body.
One problem with such apparatus is that the upper wedge surface on the conductor bore is subject to damage as tools are lowered through it. Also, there is inherently a certain amount of xe2x80x9cplayxe2x80x9d between the ratchet teeth and grooves which adds to the possibility of fatigue.
It is the object of this invention to provide such apparatus in which the upper wedge surface in the conductor bore is protected as tools are lowered through it and, more particularly in which, the body is latched with the bore in a manner which minimizes the possibility of vertical or radial movement responsive to the aforementioned forces. A more particular object is to provide such apparatus in which the latch may be easily released to permit retrieval of the body from the conductor.
These and other objects are accomplished, in accordance with illustrated and preferred embodiment of the invention, by subsea well apparatus which includes a conductor having a vertical bore therethrough, locking grooves within the bore, and a lower downwardly and inwardly tapered wedge surface within the bore beneath the grooves, and a wellhead member body which is lowerable into the bore of the conductor and which has, about its outer side, an upwardly facing seat, a recess above the seat, a lower downwardly and inwardly tapered wedge surface below the seat in the conductor bore, and an upper downwardly and inwardly tapered wedge surface between the recess and seat.
A normally contracted, split locking ring is supported on the seat and has, about its outer side, locking teeth disposable opposite the locking grooves, as the body is lowered into the conductor bore, ratchet grooves about its inner side, and an upper downwardly and inwardly tapered wedge surface beneath the ratchet grooves. A normally expanded split ratchet ring which is slidable inwardly and outwardly within the recess above the locking ring has latching teeth about its outer side, and is positioned to land on the upper end of the locking ring upon initial lowering of the body.
Upon further lowering of the body, the ratchet ring forces the locking ring and its teeth outwardly toward the locking grooves and disposes the ratchet teeth opposite the ratchet grooves. Upon still further lowering of the body, the ratchet ring forces the locking teeth into locking engagement with the locking grooves and the ratchet teeth of the ratchet ring into locking engagement with the ratchet grooves of the locking ring, as the upper wedge surface about the body tightly engages upper wedge surface on the inner side of the locking ring, and the lower wedge surface about the body tightly engages the lower wedge surface in the conductor bore. The upper and lower wedge surfaces are coaxial and extend at a relatively small angle with respect to the vertical.
The ratchet ring has a surface slidable downwardly and outwardly over a surface of the body, and the locking ring has a surface slidable upwardly and outwardly over a surface of the conductor bore, as the wedge surfaces are tightly engaged. More particularly, the first mentioned surfaces form a larger angle with respect to the horizontal than the second mentioned surfaces, so as to urge the rings outwardly with a radial component of force, thereby minimizing the possibility of gaps in the latch which might otherwise permit play leading to the possibility of fatigue.
The upper end of the locking ring extends above the conductor when the latch is set, and carries bolts for movement inwardly to force the ratchet ring into the recess and thus release its ratchet teeth from the ratchet grooves in the locking ring. Thus, the locking ring teeth are free to retract from the grooves in the conductor body to permit the rings to be raised with the body from the conductor bore.
The bore of the conductor has a reduced diameter portion beneath the first shoulder through which an enlarged portion of the body beneath the seat is guidably passed as the body is lowered, and fluid bypass slots extend vertically through one of the portions.
A normally expanded split retainer ring supported on the seat is connected to the lower end of the locking ring for expansion and contraction with respect thereto, and is releasable from the locking ring but held on the seat, as the body is initially lowered, and then reconnected to the locking ring, upon raising of the body.